摘要:

A pair of electromagnetic drift waves is shown to be excited simultaneously by an induced Cere´nkov emission by electrons. The instability is shown to be explosive. However, its property is different from the ordinary explosive instability involving three wave interactions with a negative energy wave pump. The instability here is excited by the inverted population of electrons (inverse Landau damping) and is less sensitive to the frequency mismatch or dissipation. The nonlinear growth rate is shown to exceed the linear growth rate at a reasonably small level of wave amplitude. A magnetic field perturbation is essential for this process.

ISSN:0031-9171    

DOI:10.1063/1.862082

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A simple nonlinear equation is derived to describe the pseudo‐three‐dimensional dynamics of a nonuniform magnetized plasma withTe≫Tiby taking into account the three‐dimensional electron, but two‐dimensional ion dynamics in the direction perpendicular toB0. The equation bears a close resemblance to the two‐dimensional Navier–Stokes equation. A stationary spectrum in the frequency range of drift waves is obtained using this equation by assuming a coexisting large amplitude long wavelength mode. The &ohgr;‐integratedkspectrum is given byk1.8(1+k2)−2.2, while the width of the frequency spectrum is proportional tok3(1+k2)−1, wherekis normalized bycs/&ohgr;ci. The result compares well with the recently observed spectrum in the ATC tokamak.

ISSN:0031-9171    

DOI:10.1063/1.862083

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The injection of an electron beam into a weakly collisional magnetized background plasma is investigated experimentally. The beam‐plasma system is so large that boundary effects are unimportant for establishing the current flow. It is shown that the injected beam current is balanced by a field‐aligned return current provided by background electrons drifting toward the beam source. The conditions for an ion sound instability driven by the return current are met. The maximum injected beam current is found to be limited to the background electron saturation current to the beam source.

ISSN:0031-9171    

DOI:10.1063/1.862084

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A fast electron beam is injected into an essentially collisionless magnetoplasma. The beam current closes via a field‐aligned return current which drives an ion acoustic instability. The observed frequency spectrum is close to that predicted by renormalized turbulence theory. Three‐dimensional cross‐correlation measurements exhibit a wave vector spectrum extending in magnitude tok&lgr;D≳1 and covering in direction a half‐space centered around the electron drift. Propagation of phase coherent test waves confirm the three‐dimensional character of the instability but also indicate the presence of ion drifts. These can arise from ion trapping in observed large amplitude off‐resonant beat modes generated by two obliquely propagating unstable ion acoustic waves.

ISSN:0031-9171    

DOI:10.1063/1.862085

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Anomalous current penetration into a plasma is a fundamental process which is important in a number of plasma situations included in which are the formation of discharges and current sheath layers. A recently developed two and one‐half dimensional magnetostatic code has been applied to the simulation of this process. Many anomalous processes are involved here including anomalous resistance, anomalous heat conduction, anomalous electron viscosity, and the formation of complex magnetic structures. Of dominant importance is the anomalous resistivity. It is important to identify the instabilities and turbulent processes involved. The results show that the induced current excites lower hybrid turbulence which may be related to lower hybrid oscillations recently observed in microtor. Anomalous heating and heat transport are also observed. In some cases the magnetic field lines are observed to reconnect and form magnetic islands.

ISSN:0031-9171    

DOI:10.1063/1.862070

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The instability of a planar lower hybrid soliton to transverse long wavelength perturbations is investigated numerically. Initially, a kink‐like deformation grows in agreement with linear analysis. In the nonlinear regime the soliton breaks up into bunches which move apart and spread the energy throughout the plasma.

ISSN:0031-9171    

DOI:10.1063/1.862071

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The lower‐hybrid‐drift instability is shown to be effectively stabilized by electron resonance broadening, especially in finite &bgr; plasmas. This saturation mechanism allows steady state turbulence to develop which is crucial to plasma phenomena such as magnetic field line reconnection and collisionless shock waves.

ISSN:0031-9171    

DOI:10.1063/1.862072

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A new expression for the ponderomotive force induced by high frequency electromagnetic and electrostatic waves propagating in plasma including the effects of dissipation is derived. Besides the usual irrotational leading term, a new simpler expression for the leading rotational term, which can contribute to the generation of mega‐Gauss dc magnetic fields is found. The leading irrotational term is proportional to the dissipation rate and vanishes for a standing wave. This expression is applied to the absorption of a planar electromagnetic wave, with polarization in (p) or out of (s) the plane of incidence, obliquely incident onto a half‐space of plasma with a linear density profile. The result for the dc magnetic field source term compares very well with the result from a two and one‐half dimensional particle simulation calculation forppolarization. Direct acceleration by the resonantly excited electrostatic waves is the dominant dissipation process in this case. At high power, the dominant dissipation process forspolarization is parametric decay into plasma waves which are Landau damped by the electrons. The magnetic field source term is found to be comparable to that ofppolarization.

ISSN:0031-9171    

DOI:10.1063/1.862073

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Laser generated mega‐Gauss magnetic fields may have a disordered small‐scale structure, because many different field generation mechanisms are operating simultaneously. Electron cross‐field transport in such fields is studied, concentrating on three specific nonclassical transport processes: resonant scattering, field line wandering, and an analog of neoclassical diffusion. Each of these mechanisms seems capable of producing cross‐field transport rates significantly faster than the classical values for a mega‐Gauss magnetic field, yet considerably slower than the classical value for a field‐free plasma.

ISSN:0031-9171    

DOI:10.1063/1.862074

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The equations of motion of a nearly spherical bubble immersed in an incompressible and viscous liquid are deduced using the Lagrangian procedure with a dissipation function. The results appear valid for only slightly viscous liquids.

ISSN:0031-9171    

DOI:10.1063/1.862075

出版商:AIP    

年代:1978

数据来源: AIP